Over the past 8 years our studies have focused on the characterization of functional structures on human natural killer (NK) cells in order to develop a better understanding of the role these cells play in the immune response and the mechanisms whereby NK cells exert their various effects. During this period we first developed methods for the in vitro propagation of clonal human NK cells and demonstrated the functional and phenotypic heterogeneity of these clonal populations. We also identified the NKH1 antigen (CD56) as a useful human NK cell marker that was expressed by all non-MHC restricted cytolytic effector cells in normal blood. Using NK clones, we established that the majority of NK cells do not express T cell receptor-like structures but that other structures that play important functional roles on T cells, such as CD2, CDlla/CD18, IL-2 receptors and TCR-zeta, also play critical roles in NK cell function. in each case, however, NK cells utilize these molecules in distinct ways compared to T cells. Our comparative analysis of these functional differences has led to significant insights into the cellular mechanisms by which NK cells interact with target cells as well as the mechanisms whereby NK cells themselves are regulated. The further analysis of functional structures on human NK cells, as well as the continued comparison with normal T cells, provides the basis for our proposed studies. In future studies we will examine further the role of cellular adhesion molecules (CAM) in NK cell function. Several of these structures, including CD2, CDlla/CD18, CD54, CD58 and NKH1 CD56), have been found to play important roles in the interactions between NK cells and target cells, and the differential expression of these CAM may provide a mechanism for determining the "specificity" of resting and activated effector cells. In addition, preliminary evidence suggests that these CAM may also provide a mechanism for signal transduction by NK cells. It is known that IL-2 is able to markedly enhance the cytolytic activity of NK cells, and this has led to clinical trials evaluating the anti-tumor activity of this lymphokine in patients with metastatic cancer. In order to investigate the mechanism by which IL-2 influences NK function we will characterize the role of the IL-2 receptor complex in the regulation of NK cell proliferation and cytotoxicity. In these studies we will compare effects of NK cell stimulation through either intermediate or high affinity IL-2 receptors and examine the regulation of IL-2 receptor expression and function by IL-2 itself as well as other lymphokines. In order to accomplish these goals we will utilize highly purified NK cells, in vitro activated NK cells, and NK clones obtained from normal individuals, and NK cells activated in vivo from patients receiving intravenous infusion of recombinant IL-2 for prolonged periods.